FETS and methods of forming FETS

ABSTRACT

An embodiment is a method including forming a raised portion of a substrate, forming fins on the raised portion of the substrate, forming an isolation region surrounding the fins, a first portion of the isolation region being on a top surface of the raised portion of the substrate between adjacent fins, forming a gate structure over the fins, and forming source/drain regions on opposing sides of the gate structure, wherein forming the source/drain regions includes epitaxially growing a first epitaxial layer on the fin adjacent the gate structure, etching back the first epitaxial layer, epitaxially growing a second epitaxial layer on the etched first epitaxial layer, and etching back the second epitaxial layer, the etched second epitaxial layer having a non-faceted top surface, the etched first epitaxial layer and the etched second epitaxial layer forming source/drain regions.

This application claims the benefit of U.S. Provisional Application No.62/427,599, filed Nov. 29, 2016, entitled “FETS and Methods of FormingFETS,” which patent application is incorporated herein by reference.

BACKGROUND

As the semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower costs, challenges from both fabrication and design issues haveresulted in the development of three-dimensional designs, such as a finfield effect transistor (FinFET). A typical FinFET is fabricated with athin vertical “fin” (or fin structure) extending from a substrate formedby, for example, etching away a portion of a silicon layer of thesubstrate. The channel of the FinFET is formed in this vertical fin. Agate is provided over (e.g., wrapping) the fin. Having a gate on bothsides of the channel allows gate control of the channel from both sides.However, there are challenges to implementation of such features andprocesses in semiconductor fabrication.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is an example of a Fin Field-Effect Transistor (FinFET) in athree-dimensional view.

FIGS. 2 through 6, 7A-7C, 8A-8C, and 9 through 15 are three-dimensionaland cross-sectional views of intermediate stages in the manufacturing ofFinFETs in accordance with some embodiments.

FIG. 16 is a cross-sectional view of an intermediate stage in themanufacturing of FinFETs in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Similarly, termssuch as “front side” and “back side” may be used herein to more easilyidentify various components, and may identify that those components are,for example, on opposing sides of another component. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Fin Field-Effect Transistors (FinFETs) and methods of forming the sameare provided in accordance with various embodiments. Intermediate stagesof forming FinFETs are illustrated. Some embodiments discussed hereinare discussed in the context of FinFETs formed using a gate-firstprocess. In other embodiments, a gate-last process (sometimes referredto as replacement gate process) may be used. Some variations of theembodiments are discussed. One of ordinary skill in the art will readilyunderstand other modifications that may be made that are contemplatedwithin the scope of other embodiments. Although method embodiments arediscussed in a particular order, various other method embodiments may beperformed in any logical order and may include fewer or more stepsdescribed herein.

Before addressing the illustrated embodiments specifically, certainadvantageous features and aspects of the present disclosed embodimentswill be addressed generally. In general terms, the present disclosure isa semiconductor device and method of forming the same to provide aprocess flow to achieve a non-faceted top surface for an epitaxialsource/drain in a FinFET, for device enhancement. In addition, thisnon-faceted top surface epitaxial source/drain fills the intra-fin areanear the top of the fins with the epitaxial source/drain material whichincreases the contact landing area and can reduce the contact resistanceto the source/drain region.

The process flow includes a first deposition process followed by a firstetch back process followed by a second deposition process and a secondetch back process. Each of the deposition processes can include silane(SiH₄) and phosphine (PH₃) precursors for growing, for example, siliconphosphorous (SiP) source/drain regions. Each of the etch back processesare performed in high temperature and low pressure environments and mayinclude both SiH₄ and hydrochloric acid (HCl) as a precursor. In someembodiments, the etch back processes do not include SiH4 as a precursor.The high temperature for the etch back processes may be in a range fromabout 650° C. to about 800° C. The low pressure for the etch backprocesses may be in a range from 1 torr to about 50 torr. By having theenvironment for the etch back processes be high temperature and lowpressure, the shape of the source/drain can be controlled to not have afaceted top surface as the SiH₄ will passivate the top surfaces (100orientation) while the HCl will etch the sides (110 orientation) of thesource/drain regions from about 1 to about 20 times, such as about 4times the rate of the top surfaces of the source/drain regions. A facetis a surface that is not parallel and not perpendicular to a top surfaceof the substrate. In some embodiments, the disclosed process flow can beused in the formation of static random access memory (SRAM) devices.

FIG. 1 illustrates an example of a FinFET 30 in a three-dimensionalview. The FinFET 30 includes a fin 36 on a substrate 32. The substrate32 includes isolation regions 34, and the fin 36 protrudes above andfrom between neighboring isolation regions 34. A gate dielectric 38 isalong sidewalls and over a top surface of the fin 36, and a gateelectrode 40 is over the gate dielectric 38. Source/drain regions 42 and44 are disposed in opposite sides of the fin 36 with respect to the gatedielectric 38 and gate electrode 40. FIG. 1 further illustratesreference cross-sections that are used in later figures. Cross-sectionB-B is across a channel, gate dielectric 38, and gate electrode 40 ofthe FinFET 30. Cross-section C-C is parallel to cross-section B-B and isacross a source/drain region 42. Subsequent figures refer to thesereference cross-sections for clarity.

FIGS. 2 through 15 are three dimensional and cross-sectional views ofintermediate stages in the manufacturing of FinFETs in accordance withsome embodiments. FIGS. 2 through 15 illustrate a FinFET similar toFinFET 30 in FIG. 1, except for multiple fins on a crown structure.FIGS. 2 through 6 illustrated cross-section B-B. In FIGS. 7A through 8C,figures ending with an “A” designation are three-dimensional views;figures ending with a “B” designation illustrate cross-section B-B; andfigures ending with a “C” designation illustrate cross-section C-C.FIGS. 9 through 15 illustrate cross-section C-C.

FIG. 2 illustrates a substrate 50. Substrate 50 may be a semiconductorsubstrate, such as a bulk semiconductor, a semiconductor-on-insulator(SOI) substrate, or the like, which may be doped (e.g., with a p-type oran n-type dopant) or undoped. The substrate 50 may be a wafer, such as asilicon wafer. Generally, an SOI substrate includes a layer of asemiconductor material formed on an insulator layer. The insulator layermay be, for example, a buried oxide (BOX) layer, a silicon oxide layer,or the like. The insulator layer is provided on a substrate, typically asilicon or glass substrate. Other substrates, such as a multi-layered orgradient substrate may also be used. In some embodiments, thesemiconductor material of the substrate 50 may include silicon;germanium; a compound semiconductor including silicon carbide, galliumarsenic, gallium phosphide, indium phosphide, indium arsenide, and/orindium antimonide; an alloy semiconductor including SiGe, GaAsP, AlInAs,AlGaAs, GalnAs, GaInP, and/or GaInAsP; or combinations thereof.

The substrate 50 may include integrated circuit devices (not shown). Asone of ordinary skill in the art will recognize, a wide variety ofintegrated circuit devices such as transistors, diodes, capacitors,resistors, the like, or combinations thereof may be formed in and/or onthe substrate 50 to generate the structural and functional requirementsof the design for the FinFET. The integrated circuit devices may beformed using any suitable methods.

FIG. 2 further illustrates the formation of a mask layer 52 over thesubstrate and the patterning of the substrate 50 using the mask layer 52to form a patterned portion 54 of the substrate 50. In some embodiments,the mask layer 52 is a hard mask and may be referred to as hard mask 52hereinafter. The hard mask 52 may be formed of silicon nitride, siliconoxynitride, silicon carbide, silicon carbonitride, the like, or acombination thereof.

In some embodiments, the patterned portion 54 of the substrate 50 may beformed by etching the substrate 50 that lies outside of the patternedmask layer 52. The etching may be any acceptable etch process, such as areactive ion etch (RIE), neutral beam etch (NBE), the like, or acombination thereof. The etch may be anisotropic.

FIG. 3 illustrate the formation of a crown structure 58 andsemiconductor strips 60 over the crown structure 58. A mask layer 56 maybe formed and patterned over the patterned portion 54 of the substrate50. In some embodiments, the mask layer 56 is a hard mask and may bereferred to as hard mask 56 hereinafter. The hard mask 56 may be formedof silicon nitride, silicon oxynitride, silicon carbide, siliconcarbonitride, the like, or a combination thereof.

In some embodiments, the crown structure 58 and the semiconductor strips60 may be formed by etching trenches in the hard mask 56 and thepatterned portion 54 of the substrate 50. The semiconductor strips 60may also be referred to as semiconductor fins 60. The etching may be anyacceptable etch process, such as a RIE, NBE, the like, or a combinationthereof. The etch may be anisotropic.

FIG. 4 illustrates the formation of an insulation material betweenneighboring semiconductor strips 60 to form isolation regions 62. Theinsulation material may be an oxide, such as silicon oxide, a nitride,the like, or a combination thereof, and may be formed by a high densityplasma chemical vapor deposition (HDP-CVD), a flowable CVD (FCVD) (e.g.,a CVD-based material deposition in a remote plasma system and postcuring to make it convert to another material, such as an oxide), thelike, or a combination thereof. Other insulation materials formed by anyacceptable process may be used. In the illustrated embodiment, theinsulation material is silicon oxide formed by a FCVD process. An annealprocess may be performed once the insulation material is formed. Furtherin FIG. 4, a planarization process, such as a chemical mechanical polish(CMP), may remove any excess insulation material (and, if present, thehard mask 56) and form top surfaces of the isolation regions 62 and topsurfaces of the semiconductor strips 60 that are coplanar within processvariations.

FIG. 5 illustrates the recessing of the isolation regions 62, such as toform shallow trench isolation (STI) regions. The isolation regions 62are recessed such that the upper portions of the semiconductor strips 60protrude from between neighboring isolation regions 62 and formsemiconductor fins 64. As illustrated some portions of the isolationregions 62 remains on top of the crown structure 58 between the adjacentsemiconductor fins 64. Further, the top surfaces of the isolationregions 62 may have a flat surface as illustrated, a convex surface, aconcave surface (such as dishing), or a combination thereof. The topsurfaces of the isolation regions 62 may be formed flat, convex, and/orconcave by an appropriate etch. The isolation regions 62 may be recessedusing an acceptable etching process, such as one that is selective tothe material of the isolation regions 62. For example, a chemical oxideremoval using a CERTAS® etch or an Applied Materials SICONI tool ordilute hydrofluoric (dHF) acid may be used.

The fins may be patterned by any suitable method. For example, the finsmay be patterned using one or more photolithography processes, includingdouble-patterning or multi-patterning processes. Generally,double-patterning or multi-patterning processes combine photolithographyand self-aligned processes, allowing patterns to be created that have,for example, pitches smaller than what is otherwise obtainable using asingle, direct photolithography process. For example, in one embodiment,a sacrificial layer is formed over a substrate and patterned using aphotolithography process. Spacers are formed alongside the patternedsacrificial layer using a self-aligned process. The sacrificial layer isthen removed, and the remaining spacers may then be used to pattern thefins.

FIG. 6 illustrates the formation of a gate structure over thesemiconductor fins 64. A dielectric layer (not shown) is formed on thesemiconductor fins 64 and the isolation regions 62. The dielectric layermay be, for example, silicon oxide, silicon nitride, multilayersthereof, or the like, and may be deposited or thermally grown accordingto acceptable techniques. In some embodiments, the dielectric layer maybe a high-k dielectric material, and in these embodiments, dielectriclayer may have a k value greater than about 7.0, and may include a metaloxide or a silicate of Hf, Al, Zr, La, Mg, Ba, Ti, Pb, multilayersthereof, and combinations thereof. The formation methods of dielectriclayer may include molecular-beam deposition (MBD), atomic layerdeposition (ALD), plasma-enhanced CVD (PECVD), and the like.

A gate layer (not shown) is formed over the dielectric layer, and a masklayer (not shown) is formed over the gate layer. The gate layer may bedeposited over the dielectric layer and then planarized, such as by aCMP. The mask layer may be deposited over the gate layer. The gate layermay be formed of, for example, polysilicon, although other materials mayalso be used. In some embodiments, the gate layer may include ametal-containing material such as TiN, TaN, TaC, Co, Ru, Al,combinations thereof, or multi-layers thereof. The mask layer may beformed of, for example, silicon nitride or the like.

After the layers are formed, the mask layer may be patterned usingacceptable photolithography and etching techniques to form mask 70. Thepattern of the mask 70 then may be transferred to the gate layer anddielectric layer by an acceptable etching technique to form gateelectrode 68 and gate dielectric 66. The gate electrode 68 and gatedielectric 66 cover respective channel regions of the semiconductor fins64. The gate electrode 68 may also have a lengthwise directionperpendicular, within process variation and alignment, to the lengthwisedirection of respective semiconductor fins 64.

FIGS. 7A, 7B, and 7C illustrate the formation of gate seal spacers 72 onexposed surfaces of isolation regions 62, semiconductor fins 64, gateelectrode 68, and mask 70. A thermal oxidation or a deposition processmay form the gate seal spacers 72. In some embodiments, the gate sealspacers 72 may be formed of a nitride, such as silicon nitride, siliconoxynitride, silicon carbide, silicon carbonitride, the like, or acombination thereof. The formation of the gate seal spacers 72 may befollowed by an anisotropic etch process, such as a dry etch process, toremove portions of the gate seal spacers 72 outside of the sidewalls ofthe gate structures. In some embodiments, after the etch process, someportions of the gate seal spacers 72 remains on the isolation regions 62between the adjacent semiconductor fins 64.

FIGS. 8A, 8B, and 8C illustrate the removal the semiconductor fins 64outside of the gate structure. The gate structure may be used as a maskduring the removal of the semiconductor fins 64 and such that recesses76 are formed in the semiconductor fins 64 and/or isolation regions 62.As illustrated, after the removal of the semiconductor fins 64, at leasta portion of the isolation regions 62 remains on the top surface of thecrown structure 58 between the adjacent semiconductor fins 64.

The recesses 76 may be formed by etching using any acceptable etchprocess, such as a RIE, NBE, tetramethyalammonium hydroxide (TMAH),ammonium hydroxide (NH₄OH), a wet etchant capable of etching siliconwith good etch selectivity between silicon and a material of theisolation regions 62 and/or the gate seal spacers 72, the like, or acombination thereof. The etch may be anisotropic. In some embodiments,the top surface of the crown structure 58 is exposed as at leastportions of the bottom surfaces of the recesses 76. In some embodiments,a portion of the gate seal spacer material 72 remains on the isolationregions 62 between the adjacent semiconductor fins 64 (not shown inFigures).

FIGS. 9 through 13 illustrate the formation of the source/drain regions.In some embodiments, the source/drain regions comprise multiple,distinct deposition and etch back processes. As illustrated in FIG. 9, afirst deposition process is performed to form epitaxial layer 80 in therecesses 76 by epitaxially growing a material in the recesses 76, suchas by metal-organic CVD (MOCVD), molecular beam epitaxy (MBE), liquidphase epitaxy (LPE), vapor phase epitaxy (VPE), selective epitaxialgrowth (SEG), the like, or a combination thereof. As illustrated in FIG.9, due to the blocking of the isolation regions 62 between the adjacentsemiconductor fins 64, the epitaxial layer 80 first grows vertically inrecesses 76, during which time the epitaxial layer does not growhorizontally. After recesses 76 are fully filled, the epitaxial layer 80grows both vertically and horizontally to form facets. The location ofthe fins 64 in the channel region under the gate (e.g. not recessed byprior etching step to form the recesses 76) are shown for reference.

In some exemplary embodiments in which the resulting FinFET is an n-typeFinFET, the first epitaxial layer 80 comprises silicon carbide (SiC),silicon phosphorous (SiP), phosphorous-doped silicon carbon (SiCP), orthe like. In alternative exemplary embodiments in which the resultingFinFET is a p-type FinFET, the first epitaxial layer 80 comprises SiGe,and a p-type impurity such as boron or indium.

The first epitaxial layer 80 may be implanted with dopants followed byan anneal. The implanting process may include forming and patterningmasks such as a photoresist to cover the regions of the FinFET that areto be protected from the implanting process. The first epitaxial layer80 may have an impurity concentration in a range from about 3e²¹ cm⁻³ toabout 4.2e²¹ cm⁻³. In some embodiments, the first epitaxial layer 80 maybe in situ doped during growth.

As illustrated in FIG. 9, the first epitaxial layer 80 of the adjacentsemiconductor fins merge to form a continuous epitaxial layer 80. Due tothe blocking of the isolation regions 62 on the crown structure 58, airgaps 82 are formed between the lower portions of the first epitaxiallayer 80 and the top surface of the isolation regions 62 on the crownstructure 58. After the first deposition process, the first epitaxiallayer 80 has surfaces with various crystalline orientations. Forexample, first portions 80A of the top surface of the first epitaxiallayer 80 has (100) crystalline orientations. These first portions 80Aare between second portions 80B of the top surface, which are facetsthat have (111) crystalline orientations. The faceted second portions80B of the top surface of source/drain regions 80 form between adjacentfins 64 (intra-fin area) such that the top surface of the source/drainregions 80 in the intra-fin area is below a top surface of the fins 64.The first epitaxial layer 80 also has third portions 80C, which are onthe sides of the first epitaxial layer 80 and have (110) crystallineorientations.

In FIG. 10, a first etch back process 84 is performed on the firstepitaxial layer 80. The first etch back process 84 may include multiplegases/precursors. In some embodiments, the first etch back process 84includes two precursors, SiH₄and HCl. In an embodiment, the amount ofthe SiH₄ precursor as a percentage of both of the precursors is in arange from about 5% to about 20%. In an embodiment, the amount of theHCl precursor as a percentage of both of the precursors is in a rangefrom about 10% to about 45%. In these embodiments, the SiH₄ (illustratedas the 1st precursor in FIG. 10) covers and passivates the firstportions 80A of the top surface of the first epitaxial layer 80, whichis a (100) crystalline orientation. Also, in these embodiments, the HCl(illustrated as the 2nd precursor in FIG. 10) attacks and etches thesecond and third portions 80B and 80C.

The first etch back process 84 is performed in a high temperature andlow pressure environment. The high temperature for the first etch backprocess 84 may be in a range from about 650° C. to about 800° C. The lowpressure for the first etch back process 84 may be in a range from 1torr to about 50 torr. In some embodiments, the first etch back processmay include H₂ as a carrier gas and may have an etching time in a rangefrom about 50 seconds to about 700 seconds. By having the environmentfor the etch back processes be high temperature and low pressure, theshape of the first epitaxial layer 80 can be controlled to havenon-faceted tops as the SiH₄ will passivate and protect the top surfaces(100 orientation) while the HCl precursor will attack and etch the sides(80C) (110 orientation) and faceted top surface (80B) (111 orientation)faster than the top surface (80A) (100 orientation) of the firstepitaxial layer 80. For example, the HCl will etch the sides (110orientation) of the first epitaxial layer 80 from about 1 to about 20times, such as about 4 times the rate of the top surface of the firstepitaxial layer 80. Although HCl is used as the etchant above, otheretchants, such as GeH₄ and/or Cl₂ may also be used for the controlledetch process to achieve the non-faceted top surfaces of the firstepitaxial layer. In some embodiments, the non-faceted top surface issubstantially level.

FIG. 11 illustrates the first epitaxial layer 80′ after the first etchback process 84 is performed. The etched back top surface 80A′ of thefirst epitaxial layer 80′ is a (100) crystalline orientation. In someembodiments, the intra-fin thickness of the etched back first epitaxiallayer 80′ may have a thickness T1 of about 10 nm. In some embodiments,the first etch back process 84 removes the faceted portions 80B of thetop surface to leave a top surface 80A′ that is lower than the topsurface of the fins 64 in both the fin and intra-fin areas.

FIG. 12 illustrates the second deposition process to form a secondepitaxial layer 86 on the etched back first epitaxial layer 80′. Thesecond deposition process is performed to form epitaxial layer 86 withtop surface 86A and sides 86C on the etched back first epitaxial layer80′ by epitaxially growing a material, such as MOCVD, MBE, LPE, VPE,SEG, the like, or a combination thereof. As illustrated in FIG. 12, thesecond epitaxial layer 86 grows both vertically and horizontally to formfacets on the sides 86C with the top surface 86A of the source/drainregions across the entire intra-fin area higher than the fins 64 suchthat the second epitaxial layer 86 fills the intra-fin area betweenadjacent fins. The sides 86C include facets 86C1 and 86C2 that are ondifferent planes. The facet 86C1 extends down from the top surface 86Aand meets the facet 86C2 with both facets being non-parallel andnon-perpendicular to a major surface of the substrate 50.

In some exemplary embodiments in which the resulting FinFET is an n-typeFinFET, the second epitaxial layer 86 comprises SiC, SiP, SiCP, or thelike. In alternative exemplary embodiments in which the resulting FinFETis a p-type FinFET, the second epitaxial layer 86 comprises SiGe, and ap-type impurity such as boron or indium.

The second epitaxial layer 86 may be implanted with dopants followed byan anneal. The implanting process may include forming and patterningmasks such as a photoresist to cover the regions of the FinFET that areto be protected from the implanting process. The second epitaxial layer86 may have an impurity concentration in a range from about 3e²¹ cm⁻³ toabout 4.2e²¹ cm⁻³. In some embodiments, the second epitaxial layer 86may be in situ doped during growth.

FIG. 13 illustrates the second epitaxial layer 86′ after a second etchback process with the etched back epitaxial layers 86′ and 80′ formingsource/drain regions 86′/80′. The second etch back process is similar tothe first etch back process described above and enables the secondepitaxial layer 86′ to have a top surface 86A′ higher than the fins 64in both the fin and intra-fin areas such that the second epitaxial layer86 fills the intra-fin area between adjacent fins 64. In particular, thetop surface 86A′ of the etched back second epitaxial layer 86′ can behigher than the fins 64 across the entire intra-fin area. The secondetch back process may include multiple gases/precursors. In someembodiments, the second etch back process includes two precursors, SiH₄and HCl. Further, after the second etch back process, the etched backsecond epitaxial layer 86′ can have side facets 86C3′ on the sides dueto the faster etch rate for the (110 orientation) surface of the sidesas compared to the etch rate of the top surface 86A′ (100 orientation)of the second epitaxial layer 86. The facets 86C3′ are between thefacets 86C1′ and 86C2′. In some embodiments, the facets 86C3′ aresubstantially perpendicular to a major surface of the substrate. Asdiscussed above for the first etch back process, the SiH₄ precursor willpassivate and protect the top surfaces 86A (100 orientation) while theHCl precursor will attack and etch the sides (86C) (110 orientation). Insome embodiments, the intra-fin thickness of the combined etched backfirst and second epitaxial layer 80′/86′ may have a thickness T2 ofgreater than about 10 nm. In some embodiments, the thickness T2 may betwice as thick as thickness T1, such as greater than about 20 nm.

The second etch back process is performed in a high temperature and lowpressure environment. The high temperature for the second etch backprocess may be in a range from about 650° C. to about 800° C. The lowpressure for the second etch back process may be in a range from 1 torrto about 50 torr. In some embodiments, the second etch back process mayinclude H₂ as a carrier gas and may have a etching time in a range fromabout 50 seconds to about 700 seconds. By having the environment for theetch back processes be high temperature and low pressure, the shape ofthe source/drain regions 86′/80′ can be controlled to have non-facetedtops 86A′ such that the epitaxial source/drain material fills theintra-fin area. While the top surface of the source/drain regions86′/80′ are not faceted, the lower surfaces (e.g. surfaces exposed tothe air gaps 82) are faceted surfaces.

After the formation of the source/drain regions 86′/80′, a capping layer(not shown) may formed on the source/drain regions 86′/80′. The cappinglayer may be considered part of the source/drain regions 86′/80′. Insome embodiments, the capping layer is epitaxially grown on thesource/drain regions 86′/80′. The capping layer helps to protect thesource/drain regions 86′/80′ from dopant loss during the subsequentprocessing (e.g. etching processes, temperature processing, etc.).

The epitaxial source/drain regions 86′/80′ can extend into the crownstructure 58. This portion of the source/drain regions 86′/80′ thatextends into the crown structure 58 may be referred to as a buffer layer(not shown) as it buffers the strain differences between the higherdopant concentration source/drain regions 86′/80′ above it and the crownstructure 58 below it. The buffer layer may be considered part of thesource/drain regions 86′/80′. The dopant concentration of the bufferlayer and the rest (i.e. portion of source/drain regions 86′/80′ notconsidered part of the buffer layer, e.g., portion of the source/drainregions 86′/80′ above the top surface of the crown structure 58) of thesource/drain regions 86′/80′ can be different. For example, the bufferlayer can have a lower concentration of phosphorous than the rest of thesource/drain regions 86′/80′. The higher concentration of the rest ofthe source/drain regions 86′/80′ allows for the source/drain regions86′/80′ to apply greater stress to the channel region of the FinFET.This high dopant concentration portion of the source/drain regions86′/80′ may be referred to a stressor layer 86′/80′. In addition, thedopant concentration of the capping layer and the stressor layer 86′/80′can be different.

In some embodiments, the buffer layer and the first epitaxial layer 80can be formed in a single, continuous epitaxial process. In otherembodiments, these structures may be formed in separate processes. Inthe embodiment with the single, continuous process, the processingparameters of the epitaxial process (e.g. process gas flow, temperature,pressure, etc.) can be varied to form these structures with the varyingmaterial compositions. For example, during the epitaxy, the flow rate ofthe precursors may be at a first level during the formation of thebuffer layer and may be increased to a second level when transitioningto the formation of the first epitaxial layer 80.

Subsequent processing of the FinFET device may be performed, such as theformation of one or more interlayer dielectrics and formation ofcontacts. These processes will be discussed below in reference to FIGS.14 and 15.

In FIG. 14, an interlayer dielectric (ILD) 90 is deposited over thestructure illustrated in FIG. 13. The ILD 90 is formed of a dielectricmaterial such as phosphosilicate glass (PSG), borosilicate glass (BSG),boron-doped phosphosilicate Glass (BPSG), undoped silicate glass (USG),or the like, and may be deposited by any suitable method, such as CVD,PECVD, or FCVD.

In FIG. 15, a contact 92 is formed through ILD 90. The opening forcontact 92 is formed through the ILD 90 to expose a portion of thesource/drain structure. The opening may be formed using acceptablephotolithography and etching techniques. In some embodiments, at least aportion of the capping layer, if present, and/or the etched back secondepitaxial layer 86′ is removed during the formation of the opening. Insome embodiments, the etching process for contact opening may recess theexposed portion source/drain structure (including the capping layer ifpresent) about 2 nm. A liner, such as a diffusion barrier layer, anadhesion layer, or the like, and a conductive material are formed in theopenings. The liner may include titanium, titanium nitride, tantalum,tantalum nitride, or the like. The conductive material may be copper, acopper alloy, silver, gold, tungsten, aluminum, nickel, or the like. Aplanarization process, such as a CMP, may be performed to remove excessmaterial from a surface of the ILD 90. The remaining liner andconductive material form contacts 92 in the openings. An anneal processmay be performed to form a silicide at the interface between thesource/drain regions 86′/80′ (if present, capping layer) and the contact92. In some embodiments, the silicide is formed in the recessed portionof the exposed source/drain structure discussed above. The contact 92 isphysically and electrically coupled to the source/drain regions 86′/80′(if present, capping layer).

Although not explicitly shown, a person having ordinary skill in the artwill readily understand that further processing steps may be performedon the structure in FIG. 15. For example, various inter-metaldielectrics (IMD) and their corresponding metallizations may be formedover ILD 90. Further, contacts to the gate electrode 68 may be formedthrough overlying dielectric layers.

Further, in some embodiments, a gate-last process (sometimes referred toas replacement gate process) may be used. In those embodiments, the gateelectrode 68 and the gate dielectric 66 may be considered dummystructures and will be removed and replaced with an active gate andactive gate dielectric during subsequent processing.

Although the embodiments in FIGS. 2 through 15 illustrate three fins foreach FinFET, other embodiments contemplate more or less fins for eachFinFET. Further, although the embodiments in FIGS. 2 through 15illustrate a crown structure, other structures, such as FinFETs withoutcrown structures, may also utilize the features of the currentdisclosure.

FIG. 16 is a cross-sectional view of an intermediate stage in themanufacturing of FinFETs in accordance with an exemplary embodiment.FIG. 16 illustrates cross-section C-C of FIG. 1. This embodiment issimilar to the embodiments described above in FIGS. 2 through 15 exceptthat this embodiment includes two fins on the crown structure 58.Details regarding this embodiment that are similar to those for thepreviously described embodiment will not be repeated herein.

In some embodiments, the structure in FIG. 16 may be used for an n-typemetal-oxide-semiconductor (NMOS) transistor in an SRAM device. Forexample, the device in FIG. 16 may be used as a pull-down transistor inthe SRAM device. In this embodiment, the source/drain regions 80 maycomprise SiC, SiP, SiCP, or the like. Similar to the previousembodiments, some portion of the isolation regions 62 remains near theopening of the recess that is formed when the semiconductor fin 64 isetched back. This remaining isolation region 62 helps to form the airgaps 82 between adjacent semiconductor fins 64. Also similar to theprevious embodiments, by having the environment for the etch backprocesses be high temperature and low pressure, the shape of thesource/drain regions 86′/80′ can be controlled to have non-faceted tops86A′ such that the epitaxial source/drain material fills the intra-finarea.

Although not shown, this embodiment can also include the remainingportion of the gate seal spacer 72 on the remaining portion of theisolation region 62 between the adjacent fins.

Embodiments may achieve advantages. For example, the present disclosureis a semiconductor device and method of forming the same to provide aprocess flow to achieve a non-faceted epitaxial source/drain in a FinFETfor device enhancement. In addition, this non-faceted epitaxialsource/drain increases the contact landing area which can reduce thecontact resistance to the source/drain region.

The process flow includes a first deposition process followed by a firstetch back process followed by a second deposition process and a secondetch back process. Each of the deposition processes includes silane(SiH4) as a precursor for growing, for example, silicon phosphorous(SiP) source/drain regions. Each of the etch back processes areperformed in high temperature and low pressure environments and mayinclude SiH4 as a precursor and hydrochloric acid (HCl) as a precursor.In some embodiments, the etch back processes do not include SiH4 as aprecursor. The high temperature for the etch back processes may be in arange from about 650° C. to about 800° C. The low pressure for the etchback processes may be in a range from 1 torr to about 50 torr. By havingthe environment for the etch back processes be high temperature and lowpressure, the shape of the source/drain can be controlled to havenon-faceted tops as the SiH4 will passivate the top surfaces (100orientation) while the HCl will etch the sides (110 orientation) of thesource/drain regions from about 1 to about 20 times, such as about 4times the rate of the top surfaces of the source/drain regions. In someembodiments, the disclosed process flow can be used in the formation ofstatic random access memory (SRAM) devices.

An embodiment is a method including: forming a raised portion of asubstrate; forming fins on the raised portion of the substrate; formingan isolation region surrounding the fins, a first portion of theisolation region being on a top surface of the raised portion of thesubstrate between adjacent fins; forming a gate structure over the fins;and forming source/drain regions on opposing sides of the gatestructure, wherein forming the source/drain regions includes:epitaxially growing a first epitaxial layer on the fin adjacent the gatestructure; etching back the first epitaxial layer; epitaxially growing asecond epitaxial layer on the etched first epitaxial layer; and etchingback the second epitaxial layer, the etched second epitaxial layerhaving a non-faceted top surface, the etched first epitaxial layer andthe etched second epitaxial layer forming source/drain regions. In anembodiment, the method further includes an air gap separating at leastone source/drain region from the first portion of the isolation region.In an embodiment, the method further includes forming a gate seal spaceron sidewalls of the gate structure, a first portion of the gate sealspacer being between the first portion of the isolation region and theair gap. In an embodiment, the forming the source/drain regions furtherincludes: recessing the fins outside of the gate structure to have topsurfaces below a top surface of the isolation region; and epitaxiallygrowing the first epitaxial layer from the recessed fins on opposingsides of the gate structures. In an embodiment, the first epitaxiallayer and the second epitaxial layer include silicon phosphorous (SiP).In an embodiment, the etching back the first epitaxial layer and etchingback the second epitaxial layer are performed in an environment having afirst temperature and at a first pressure, the first temperature beingin a range from 650° C. to 800° C. and the first pressure being in arange from 1 torr to 50 torr. In an embodiment, the etching back thefirst epitaxial layer and etching back the second epitaxial layerincludes etching the first epitaxial layer and the second epitaxiallayer with hydrochloric acid. In an embodiment, after epitaxiallygrowing the first epitaxial layer on the fin adjacent the gate structureand before etching back the first epitaxial layer, a top surface of thefirst epitaxial layer has first facets, wherein the etching back thefirst epitaxial layer removes the first facets. In an embodiment, thefirst facets have (111) crystalline orientations. In an embodiment,after etching back the first epitaxial layer, a top surface of theetched first epitaxial layer is lower than the top surface of the finsin a fin area and in an area between adjacent fins. In an embodiment,after etching back the second epitaxial layer, the non-faceted topsurface of the etched second epitaxial layer is higher than the topsurface of the fins in the fin area and in the area between adjacentfins.

Another embodiment is a method including: forming a first fin over asubstrate; forming an isolation region surrounding the first fin;forming a first gate structure over the first fin; recessing the firstfin outside of the first gate structure to have a top surface below atop surface of the isolation region; and forming a first source/drainregion from the recessed first fin outside of the first gate structure,wherein forming the first source/drain region includes: epitaxiallygrowing a first epitaxial layer from the recessed first fin adjacent thefirst gate structure; etching back the first epitaxial layer with afirst etch back process, the first etch back process including SiH4 andHCl; epitaxially growing a second epitaxial layer on the etched firstepitaxial layer; and etching back the second epitaxial layer with asecond etch back process, the second etch back process including SiH4and HCl, the etched first epitaxial layer and the etched secondepitaxial layer forming the first source/drain region. In an embodiment,the method further includes forming a gate seal spacer on sidewalls ofthe first gate structure, a first portion of the gate seal spacer beingon the isolation region, the first portion of the gate seal spacerhaving a top surface above a top surface of the recessed first fin. Inan embodiment, the method further includes forming a second fin over thesubstrate, the second fin being adjacent the first fin, the isolationregion surrounding the second fin, the first gate structure being overthe second fin; recessing the second fin outside of the first gatestructure to have a top surface below a top surface of the isolationregion; and epitaxially growing a second source/drain region from therecessed second fin outside of the first gate structure, the firstsource/drain region and the second source/drain region merge together toform a continuous source/drain region, the isolation region forming anair gap between a top surface of the isolation region and the continuoussource/drain region. In an embodiment, the method further includesforming a gate seal spacer on sidewalls of the first gate structure, afirst portion of the gate seal spacer being on the isolation region, thefirst portion of the gate seal spacer being between the air gap and theisolation region. In an embodiment, the the first epitaxial layer andthe second epitaxial layer include silicon phosphorous (SiP).

A further embodiment is a structure including: a raised portion of asubstrate; a first fin over the raised portion of the substrate; asecond fin over the substrate, the second fin being adjacent the firstfin; an isolation region surrounding the first fin and the second fin; agate structure along sidewalls and over upper surfaces of the first finand the second fin; a source/drain region on the first fin and thesecond fin adjacent the gate structure, the source/drain region having anon-faceted top surface; and an air gap separating the source/drainregion from a top surface of the raised portion of the substrate. In anembodiment, the non-faceted top surface of the source/drain region ishigher than top surfaces of the first fin and the second fin in an areabetween the first fin and the second fin. In an embodiment, thesource/drain region includes silicon phosphorous (SiP). In anembodiment, the structure further includes a first portion of theisolation region is between the air gap and the top surface of theraised portion of the substrate.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: forming a raised portion ofa substrate; forming fins on the raised portion of the substrate;forming an isolation region surrounding the fins, a first portion of theisolation region being on a top surface of the raised portion of thesubstrate between adjacent fins; forming a gate structure over the fins;and forming source/drain regions on opposing sides of the gatestructure, wherein forming the source/drain regions comprises:epitaxially growing a first epitaxial layer on the fins adjacent thegate structure; etching back the first epitaxial layer; epitaxiallygrowing a second epitaxial layer on the etched first epitaxial layer;and etching back the second epitaxial layer, the etched second epitaxiallayer having a non-faceted top surface and faceted side surfaces, eachof the faceted side surfaces having a first facet, a second facet, and athird facet, the first facet and the third facet being non-parallel andnon-perpendicular to a major surface of the substrate, the second facetbeing between the first facet and the third facet, the second facetbeing perpendicular to the major surface of the substrate, the etchedfirst epitaxial layer and the etched second epitaxial layer formingsource/drain regions.
 2. The method of claim 1 further comprising an airgap separating at least one source/drain region from the first portionof the isolation region.
 3. The method of claim 2 further comprising:forming a gate seal spacer on sidewalls of the gate structure, a firstportion of the gate seal spacer being between the first portion of theisolation region and the air gap.
 4. The method of claim 1, wherein theforming the source/drain regions further comprises: recessing the finsoutside of the gate structure to have top surfaces below a top surfaceof the isolation region; and epitaxially growing the first epitaxiallayer from the recessed fins on opposing sides of the gate structures.5. The method of claim 1, wherein the first epitaxial layer and thesecond epitaxial layer comprise silicon phosphorous (SiP).
 6. The methodof claim 1, wherein the etching back the first epitaxial layer andetching back the second epitaxial layer are performed in an environmenthaving a first temperature and at a first pressure, the firsttemperature being in a range from 650° C. to 800° C. and the firstpressure being in a range from 1 torr to 50 torr.
 7. The method of claim1, wherein the etching back the first epitaxial layer and etching backthe second epitaxial layer comprises etching the first epitaxial layerand the second epitaxial layer with hydrochloric acid.
 8. The method ofclaim 1, wherein after epitaxially growing the first epitaxial layer onthe fin adjacent the gate structure and before etching back the firstepitaxial layer, a top surface of the first epitaxial layer has firstfacets, wherein the etching back the first epitaxial layer removes thefirst facets.
 9. The method of claim 8, wherein the first facets have(111) crystalline orientations.
 10. The method of claim 1, wherein afteretching back the first epitaxial layer, a top surface of the etchedfirst epitaxial layer is lower than the top surface of the fins in a finarea and in an area between adjacent fins.
 11. The method of claim 10,wherein after etching back the second epitaxial layer, the non-facetedtop surface of the etched second epitaxial layer is higher than the topsurface of the fins in the fin area and in the area between adjacentfins.
 12. A method comprising: forming a first fin over a substrate;forming an isolation region surrounding the first fin; forming a firstgate structure over the first fin; recessing the first fin outside ofthe first gate structure to have a top surface below a top surface ofthe isolation region; forming a first source/drain region from therecessed first fin outside of the first gate structure, wherein formingthe first source/drain region comprises: epitaxially growing a firstepitaxial layer from the recessed first fin adjacent the first gatestructure; etching back the first epitaxial layer with a first etch backprocess, the first etch back process including silane and hydrochloricacid; epitaxially growing a second epitaxial layer on the etched firstepitaxial layer; and etching back the second epitaxial layer with asecond etch back process, the second etch back process including silaneand hydrochloric acid, the etched first epitaxial layer and the etchedsecond epitaxial layer forming the first source/drain region; forming asecond fin over the substrate, the second fin being adjacent the firstfin, the isolation region surrounding the second fin, the first gatestructure being over the second fin; recessing the second fin outside ofthe first gate structure to have a top surface below a top surface ofthe isolation region; and epitaxially growing a second source/drainregion from the recessed second fin outside of the first gate structure,the first source/drain region and the second source/drain region mergetogether to form a continuous source/drain region, the isolation regionforming an air gap between a top surface of the isolation region and thecontinuous source/drain region.
 13. The method of claim 12 furthercomprising: forming a gate seal spacer on sidewalls of the first gatestructure, a first portion of the gate seal spacer being on theisolation region, the first portion of the gate seal spacer having a topsurface above a top surface of the recessed first fin.
 14. The method ofclaim 12 further comprising: forming a gate seal spacer on sidewalls ofthe first gate structure, a first portion of the gate seal spacer beingon the isolation region, the first portion of the gate seal spacer beingbetween the air gap and the isolation region.
 15. The method of claim12, wherein the first epitaxial layer and the second epitaxial layercomprise silicon phosphorous (SiP).
 16. A method comprising: forming afirst fin over a substrate; forming an isolation region surrounding thefirst fin; forming a gate structure over the first fin; and formingsource/drain regions on opposing sides of the gate structure, whereinforming the source/drain regions comprises: epitaxially growing a firstepitaxial layer on the first fin adjacent the gate structure; etchingback the first epitaxial layer; epitaxially growing a second epitaxiallayer on the etched first epitaxial layer; and etching back the secondepitaxial layer, the etched first epitaxial layer and the etched secondepitaxial layer forming source/drain regions, an air gap between atleast one source/drain region and a top surface of the isolation region.17. The method of claim 16 further comprising: forming a gate sealspacer on sidewalls of the gate structure, a first portion of the gateseal spacer being between the isolation region and the air gap.
 18. Themethod of claim 16, wherein the forming the source/drain regions furthercomprises: recessing the first fin outside of the gate structure to havetop surfaces below a top surface of the isolation region; andepitaxially growing the first epitaxial layer from the recessed fins onopposing sides of the gate structures.
 19. The method of claim 16,wherein after epitaxially growing the first epitaxial layer on the firstfin adjacent the gate structure and before etching back the firstepitaxial layer, a top surface of the first epitaxial layer has firstfacets, wherein the etching back the first epitaxial layer removes thefirst facets, and wherein after etching back the second epitaxial layer,the etched second epitaxial layer has a non-faceted top surface.
 20. Themethod of claim 16, wherein the etching back the first epitaxial layerand etching back the second epitaxial layer comprises etching the firstepitaxial layer and the second epitaxial layer with silane andhydrochloric acid.